The Digital Video Broadcasting-Terrestrial standard (DVB-T) utilises Orthogonal Frequency Division Multiplexing (OFDM) to communicate data representing video images and sound to receivers via a broadcast radio communications signal. The DVB-T standard provides for two modes of operation, which are known as the 2 k and the 8 k mode. The 2 k mode provides 2048 possible sub-carriers whereas the 8 k mode provides 8192 possible sub-carriers. Similarly for the Digital Video Broadcasting-Handheld standard (DVB-H) a 4 k mode has been provided, in which the number of possible sub-carriers is 4096. For each of these modes a number of sub-carriers for communicating data is defined in accordance with the total number of sub-carriers available in each mode.
In order to improve the integrity of data communicated using DVB-T or DVB-H a symbol interleaver is provided in order to interleave input data symbols as these symbols are mapped onto the sub-carrier signals of an OFDM symbol. Such a symbol interleaver comprises an interleaver memory in combination with an address generator. The address generator generates an address for each of the input symbols, each address indicating one of the sub-carrier signals of the OFDM symbol onto which the data symbol is to be mapped. For the 2 k mode and the 8 k mode an arrangement has been disclosed in the DVB-T standard for generating the addresses for the mapping. Likewise for the 4 k mode of DVB-H standard, an arrangement for generating addresses for the mapping has been provided and an address generator for implementing this mapping is disclosed in European Patent application 04251667.4. The address generator comprises a linear feed back shift register which is operable to generate a pseudo random bit sequence and a permutation circuit. The permutation circuit permutes the order of the content of the linear feed back shift register in order to generate an address. The address provides an indication of one of the OFDM sub-carriers for carrying an input data symbol stored in the interleaver memory, in order to map the input symbols onto the sub-carrier signals of the OFDM symbol.
Although the arrangement of the interleavers for each of the different operating modes has been defined for the Digital Video Broadcasting-Terrestrial broadcasting standard, other communications applications could also benefit from the efficiency with which data is communicated using the DVB standard. One example might be a standard associated with communicating audio, video and data via cable.